The long-term objective of this project is to establish the mechanism by which catecholamine biosynthesis is regulated. It will provide some of the basic knowledge necessary for a rational approach to certain cardiovascular diseases, such as hypertension and to some psychiatric problems, such as the affective disorders. We are particularly interested in studying the molecular mechanism of the feedback control and the possible allosteric properties of tyrosine hydroxylase. Attempts will be made to purify tyrosine hydroxylase from sources other than bovine adrenal gland because previous attempts with this tissue were unsuccessful. Since it is known that the concentration of reduced pteridines can determine the rate of hydroxylation of tyrosine to dopa, we will also study the importance of dihydropteridine reductase in the regulation of catecholamine synthesis. A direct method to measure the activity of dihydropteridine reductase will be developed and the kinetic characteristics of the enzyme will be studied. The possibility of inhibiting dihydropteridine reductase in vitro and in vivo will be explored.